engleski

Co-occurrence of functional groups in phytoplankton assemblages dominated by diatoms and chrysophytes

Abstract Phytoplankton assemblages of four deep karstic lakes in Croatia and the ecological conditions correlating to those assemblages during succession period were investigated. Samples from lakes Prošće, Kozjak, Visovac and Vransko were taken monthly throughout 2009 and 2010 at 5 m intervals from the surface to the bottom in the deepest part of the lakes. Species with high affinity for nutrients or capability of mixotrophy dominated in all investigated habitats. Changes in the structure of the community reflecting dominant interannual succession in phytoplankton assemblages for each lake were caused by the same taxa: Cyclotella, Dinobryon, Ceratium/Peridinium, except for Lake Visovac where Oocystis was also well represented. Statistical analyses confirmed that these common taxa reflect conditions in the oligo-mesotrophic habitats. It is considered that the functional approach by Reynolds is a method that captures much of the species ecology, and therefore can be successfully used as a method of describing successions. Results of its application on the phytoplankton communities of deep karstic lakes confirmed association E, with Dinobryon species as descriptive representatives, as main functional group in lakes Prošće and Vransko. Group B, with Cyclotella as a descriptive genus, dominated in lakes Kozjak and Visovac. Functional groups B (A), E and L0 co-occurred in 50-90% of samples for all investigated habitats. Those three functionally well-adapted groups interchange in dominance during seasonal cycle and, thus, likely tolerate the constraining conditions of nutrients deficiency more successfully as an aggregated group. The fact that three groups describe such high percentage of community variation additionally accentuates the importance and applicability of functional groups. Do we marginalize the role of species biodiversity by applying the functional groups and then aggregating multitudes of different groups? Aggregating species into groups can be largely subjective process and can provide only selective information about individual species observed in the field. Also, aggregation of functional groups in our systems puts conclusions at a greater distance from empirical results, so it seems reasonable to propose a hybrid approach that relies on simple model of the species taxonomical classes and functional classification, which can successfully describe a variety of species in deep karstic lakes.

phytoplankton assemblages; functional classification; deep karstic lakes

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